Configuring HTTP/2 Protocol
1. Enabling HTTP/2 Module
| Directive | Values | Description |
|---|---|---|
| LoadModule | http2_module modules/mod_http2.so |
Load the HTTP/2 module into Apache |
| Protocols | h2 http/1.1 |
Enable HTTP/2 and fallback to HTTP/1.1 |
Note: Ensure
mod_http2 is installed and enabled in your Apache build.
2. Configuring HTTP/2 Protocol
| Directive | Description | Values | Notes |
|---|---|---|---|
| Protocols | Enables or disables HTTP/2 and other protocols | http/1.1, h2, h2c |
Use h2 to enable HTTP/2 over TLS, h2c for cleartext HTTP/2 |
| ProtocolsH2 | Enables HTTP/2 over TLS only | on, off |
Deprecated in favor of Protocols |
| H2MaxWindowSize | Maximum window size for HTTP/2 streams | integer |
Default is 65535 bytes |
| H2MaxConcurrentStreams | Maximum number of concurrent streams per connection | integer |
Default is 100 |
Example: Enabling HTTP/2 with TLS
<VirtualHost *:443>
SSLEngine on
SSLCertificateFile /path/to/cert.pem
SSLCertificateKeyFile /path/to/key.pem
Protocols h2 http/1.1
</VirtualHost>Example: Enabling HTTP/2 with ALPN
<VirtualHost *:443>
SSLEngine on
SSLCertificateFile /path/to/cert.pem
SSLCertificateKeyFile /path/to/key.pem
Protocols h2 http/1.1
SSLProtocol all -SSLv2 -SSLv3
SSLCipherSuite ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384
</VirtualHost>3. Using HTTP/2 over TLS
| Directive | Description | Default | Notes |
|---|---|---|---|
| Protocols | Enables or disables specific protocols including HTTP/2 | http/1.1 |
Must include h2 to enable HTTP/2 |
| ProtocolsH2 | Enables HTTP/2 only (disables HTTP/1.1) | Off | Requires TLS to be enabled |
| H2Direct | Enables HTTP/2 direct (without ALPN) | Off | Not recommended for production use |
Example: Enabling HTTP/2 with TLS
<VirtualHost *:443>
ServerName example.com
SSLEngine on
SSLCertificateFile /path/to/cert.pem
SSLCertificateKeyFile /path/to/key.pem
Protocols h2 http/1.1
</VirtualHost>
Note: HTTP/2 requires TLS 1.2 or higher and is not supported over plain HTTP.
Warning: Ensure that your SSL/TLS configuration supports HTTP/2. Older cipher suites may not be compatible.
4. Configuring HTTP/2 Cleartext
| Directive | Description | Default | Notes |
|---|---|---|---|
| Protocols | Enables or disables specific protocols including HTTP/2 | http/1.1 |
Must include h2 to enable HTTP/2 |
| ProtocolsH2 | Enables HTTP/2 protocol only | Disabled | Available in Apache 2.4.23+ |
Example: Enabling HTTP/2 Cleartext
<VirtualHost *:80>
ServerName example.com
Protocols h2 http/1.1
DocumentRoot /var/www/html
</VirtualHost>
Note: HTTP/2 over cleartext (port 80) requires the
Protocols directive and is not enabled by default.
Warning: HTTP/2 over cleartext is not secure and should only be used in development or internal networks.
5. Setting Stream Window Size
| Directive | Values | Description |
|---|---|---|
| Http2StreamWindowSize | 65536 to 2147483647 |
Defines the initial window size (in bytes) for HTTP/2 streams. Default is 65536 bytes. |
Example: Setting Stream Window Size
<IfModule mod_http2.c>
Http2StreamWindowSize 1048576
</IfModule>
Note: Increasing the stream window size can improve performance for large file transfers but may increase memory usage.
6. Configuring Server Push
| Directive | Description | Values | Notes |
|---|---|---|---|
| Protocols | Enables HTTP/2 protocol support | h2, h2c |
Must be enabled to use server push |
| Push | Enables or disables server push | on, off |
Default is off |
| PushProvider | Specifies the provider for server push | default, none |
Default is default |
Example: Enabling Server Push
<VirtualHost *:443>
ServerName example.com
Protocols h2 h2c
Push on
PushProvider default
</VirtualHost>
Note: Server push is an HTTP/2 feature that allows the server to send resources to the client before they are explicitly requested, potentially improving page load times.
7. Setting Max Concurrent Streams
| Directive | Values | Description |
|---|---|---|
| H2MaxConcurrentStreams | 100 |
Maximum number of concurrent streams per connection for HTTP/2 |
Example: Configuring Max Concurrent Streams
<IfModule mod_http2.c>
H2MaxConcurrentStreams 100
</IfModule>8. Configuring HTTP/2 Timeout
| Directive | Values | Description |
|---|---|---|
| H2MaxWorkerIdleSeconds | 60 |
Maximum idle time for an HTTP/2 worker thread before it is terminated. Default is 60 seconds. |
| H2MaxWorkers | 100 |
Maximum number of HTTP/2 worker threads to use. Default is 100. |
| H2MinWorkers | 5 |
Minimum number of HTTP/2 worker threads to keep active. Default is 5. |
| H2MaxStreamsWithoutData | 1000 |
Maximum number of streams that can be open without sending data. Default is 1000. |
Note: These directives are part of the
mod_http2 module and require Apache 2.4.35 or later.
9. Setting Priority Handling
| Directive | Description | Default | Notes |
|---|---|---|---|
| HTTP2MaxReservedStreams | Maximum number of reserved streams per connection | 100 |
Controls how many streams can be reserved at once |
| HTTP2StreamMaxAge | Maximum age of a stream in seconds before it is closed | 300 |
Helps manage resource usage on long-lived connections |
| HTTP2MaxConcurrentStreams | Maximum number of concurrent streams per connection | 100 |
Enforces limits on concurrent stream handling |
Example: Configuring HTTP/2 Stream Limits
<IfModule mod_http2.c>
HTTP2MaxReservedStreams 50
HTTP2StreamMaxAge 600
HTTP2MaxConcurrentStreams 150
</IfModule>
Note: These directives are only available when
mod_http2 is enabled and configured.
10. Using Early Hints
| Directive | Description | Values | Notes |
|---|---|---|---|
| HTTP2EarlyHint | Enables or disables Early Hints support | on, off |
Available in Apache 2.4.52+ |
Note: Early Hints are part of HTTP/2 and require a compatible client to benefit from the performance improvements.
11. Testing HTTP/2 Support
| Flag | Description | Notes |
|---|---|---|
| --http2 | Enables HTTP/2 for the request | Requires curl built with nghttp2 |
| --http2-prior-knowledge | Assumes HTTP/2 support without negotiation | Useful for known HTTP/2 servers |
Note: Ensure the server is configured to support HTTP/2 via
Protocols directive in Apache.
Warning: HTTP/2 requires TLS (HTTPS) to function properly.
12. Troubleshooting HTTP/2 Issues
| Issue | Possible Cause | Solution |
|---|---|---|
| No HTTP/2 support | Module not loaded or OpenSSL version too old | Ensure mod_http2 is loaded and OpenSSL >= 1.0.2 |
| Slow response times | Server configuration not optimized for HTTP/2 | Adjust MaxConnectionsPerChild, KeepAliveTimeout |
| Mixed content errors | HTTP/2 with HTTP 1.1 resources | Ensure all assets are served over HTTP/2 or use Upgrade-Insecure-Requests |
| Connection resets | Client or server timeout settings too low | Increase Timeout and KeepAliveTimeout |
Example: Enabling HTTP/2 with mod_http2
<VirtualHost *:443>
SSLEngine on
SSLCertificateFile /path/to/cert.pem
SSLCertificateKeyFile /path/to/key.pem
Protocols h2 http/1.1
H2MaxSessionMem 65536
</VirtualHost>
Note: HTTP/2 requires TLS (HTTPS) to function properly.
Warning: Some older browsers do not support HTTP/2. Ensure fallbacks are in place.